Internal Tester does not get API response form the app on his device

We are building an app that accesses API data from a https protected server. The API key is all ok on my side, either installing the app through Xcode or through TestFlight, on my devices, everything works. However when my partner installs the app for testing on his device (iOS version compatible) according to crash reports, he does not get API data. The API is a paid API and we have a lot of calls left on our plan. I have verified if there were any issues with encryption compliance, and from what I have, we are ERA compliant. I don't know what else to do or check.